1. Field of the Invention
This invention relates to a punch press, and more particularly to a numerically controlled punch press having rotatable punch and die holders respectively accommodating a punch and the corresponding die, the punch being maintained at a predetermined angular attitude relative to the die throughout the punching operation.
2. Description of the Prior Art
In an NC punch press, a workpiece to be worked is set in a punching position according to programmed control and is subjected to the punching or shearing operation by a punch tool.
With a conventional NC punch press, a rectangular shape such as shown at A of FIG. 15 can be effectively cut out using a pair of punch and die of the shapes as shown at a while positioning the workpiece in both the X and Y axes. However, it is impossible to cut out such a part of an annular shape as shown at B with only a pair of punch and die of the shapes as shown at b. Thus, it is necessary to replace one tool with another merely for the purpose of changing angular attitude thereof. Such replacement is time-consuming and spoils the important feature of the NC punch press that it is capable of 100 to 500 times of punching operations in one minute. A turrent punch press can improve the problem in the machining time to some extent, but it can mount only a limited number of punch tools so that it is difficult to obtain a smooth curved cut line.